I had a period when I was young where my grocery budget was $30 per week. That lasted for over two years. Many lentils and much brown rice were consumed. Also tofu, which was extraordinarily cheap back then, and for empty calories, there was ramen. I started a herb garden and ate lots of green leafy vegetables. I invested in some spices, and could buy fish off the boat for next to nothing. I ended that period of poverty fit and healthy, but it was a constant, precarious struggle, the diet was monotonous, and shopping and cooking required considerable effort on top of working fulltime.

I wouldn't like to go back to it, but I could if I had to. Sometime I'll work out how much it'd cost to do that now.